Method of and apparatus for coating cathodes



Oct. 22, 1929. g MccULLOUGH lumen or AND APPARATUS FOR comm: cnnomas Filed May 14, 1925 @y g m 5 Patented Oct. 22, 1929 PATENT OFFICE FREDERICK S. MCCULLOUGH, PF WILKINSBURG, PENNSYLVANIA METHQD OF AND APPARATUS FOR COATING CATHODES Application filed May 14,

The present invention relates to the coatin of cathode structures for use in electron tu es.

In certain types of thermionic tubes,. the cathode is in the form of a metal sleeve which surrounds and is fitted on a suitable heating element. In order to get the best results, it is desirable to coat these sleeves with an emitting substance. As such emitting substance has to be baked onto'the metal of the oathode, and as metals desirable for this purpose are of a readily oxidizable nature, and as the an apparatus for practicing the invention;

.Fig. 2 is a plan view of a part of the dipping rack;

Fig. 3 is a broken side view .of the dipping rack, showing cathodes in place thereon;

Fig. 4 is a detail view of one of the cathodes. As the nature of the invention may be best understood by understanding the structure of the cathode, reference may be first made to Fig. 4. In this figure, A is a metal sleeve, preferably continuously cylindrical and preferably formed of th n sheet metal of a'suitable nature. Nickel is referably used as the metal for the sleeve. elded or otherwise secured to the sleeve is a lead'wire or stem B of a suitable nature.

In practicing the invention, the sleeves A are first preferably treated to drive out the contained gases, particularly air. This may be done by baking in a suitable apparatus,

either in a vacuum or in a suitable atmosphere of inert gas, such as hydrogen. When the air is driven out of the metal, it is not rapidly absorbed again, and the sleeves may be exosed to air for a considerable time without injury.

1925. Serial No. 80,181.

After being so treated, the stems or wires B are attached. The cathodes are then threaded or arranged end-to-end on wires 5 havmg head fportions 6 on their upper ends. T hese wires orm a removable part of a dip- 56 ping rack. This dipping rack has a central rod or stem 7 having two spaced apart disks 8 and 9 thereon, the lower disk 9 being at or near the bottom of the stem.

These disks are of the form shown in Fig. 2, having radial notches 10 therein, which are preferably enlarged at their inner ends. The tops of the wires 5 slip into the notches of the upper disk, while the heads 6 thereof prevent them from slipping down.,. The lower ends of the wires are received in the notches of the lower disk, retaining the cathodes on the wires and holding the lower ends of the wires in spaced relation. Fig. 3 clearly illustrates the construction of the rack and the manner of placing the cathodes thereon.

When the desired number of cathodes have been arranged on the rack, they may be coated. To this en a special apparatus such as that shown in Fig. 1 has been designed.

The apparatus includes an upper casing 11 of glass or other suitable material, open at its top and bottom. Alayer of insulating material may surround the lower portion of the casing, and within this layer of insulatso ing material is a coil 12 in circuit with a suitable source 13 of high frequency current. The part of the casing surrounded by the coil forms the baking or heating chamber, while the portion 11" extending above the heating chamber is a cooling chamber. Fitted into the lower end of the outer casing, and'preferably detachable therefrom, is a cylindrical container 14. This container is of suflicient depth to contain sufiicient liquid to enable the sleeve carrying portion of the dipping rack to be immersed. At the bottom of the receptacle is an inlet pipe 15.

The receptacle is filled to a sufiicient depth with a solution or thin paste containing the coating compound, such as an alkaline earth carbonate and water. The carbonate is finely divided or comminuted so as to readily stay in suspension in the liquid. This may be kept in a constant state of agitation by the introduction of an inert gas such as carbon dioxide through the inlet pipe 15. This gas not only keeps the mixture or solution agitated, but fills the interior of the upper casing 11 and 11'.

The rack charged "with cathodes is lowered into the apparatus as shown in Fig. 1, until the rack is immersed in the coating mixture in the receptacle. The rack is then raised into ihe upper casing and the coil 12 is enerize g The oscillating field setup by the coils effects a heating of the cathodes and bakes the coating material thereon. taken, however, to so control the baking or heat treatment that the temperature thereof does not cause the oxidation of the nickel or metal of the cathode. After the coating has been baked on, the rack is raised out of the furnace through the upper extension 11', where they cool in an atmosphere of CO gas before being taken out into the air.

' Obviously any suitable heating means could be substituted for the radio-frequency coil, although the temperature can be quite acclurately controlled with a radio frequency CO1 I have illustrated a preferred form of my invention, but it will be understood that various changes are contemplated under the scope and spirit of the invention.

I claim as my invention: 7

1.. The method of coating oxidizable cathode bodies which consists in immersing the bodies in a coating bath. and immediately baking the adherent coating in an atmos-' phere of inert gas, and then cooling said.

cathode in said inert gas.

2. The method of coating oxidizable metal cathodes which consists in immersing the cathodes into a coating paste, raising the cathodes out of the paste into a heating chamber and baking on the adherent coating .in an atmosphere of inert gas, and cooling the cathodes in an atmosphere of inert gas.

3. The method of coating oxidizable metal cathodes which consists in immersing the cathodes in a coating paste, raising the cathodes vertically into a heating chamber and baking on the adhering coating while in an atmosphere of carbon dioxide gas, and then raising the cathodes through a chamber containing an atmosphere of carbon dioxide.

4. The method of coating metallic cathode bodies which consists in driving out absorbed air from the bodies, dipping the bodies in a coating bath, and baking the adhering coating in an atmosphere of inert gas, and then raising the cathode into .a chamber containing the inert gas.

5. An apparatus for coating cathodes comprising a baking furnace, a dipping vessel at at bottom of the furnace and forming a continuation thereof, and a cooling chamber at Care must maaoaa the top of the furnace ma forming a continnation thereof.

6. An apparatus for the coating of cathodes comprising an elongated vertical fur nace having a vertical 0 amber therein, an

elongated receptacle containing a coating bath removably connected with the bottom thereof and forming an extension thereof, and means connecte to said receptacle for introducing gas into said receptacle near the lower end thereof.

An a paratus for coating cathodes comprlsmg a aking furnace, a dlpping vessel at the. bottom of the furnace, and forming a continuation thereof, a cooling chamber at the top of the furnace and forming a continuation thereof, and means connected to said dipping vessel for sup lying carbon dioxide gas to the lower en of the dipping vessel, said apparatus having an opening at its top.

In testimony whereof I hereunto aflix my signature.

. FREDERICK s. MoCUL LOUGH. 

